The present invention relates to a feathering propeller the pitch of which can be manually adjusted and which is particularly suited for sailing-boats.
The use of feathering propellers in sailing-boats for reducing drag when the boat is moving under sail is common.
On the other hand, in order to achieve the maximum efficiency in motor-driven motion, the propeller should be designed in function of the mechanical characteristics of the engine used (torque and power characteristics in function of the r.p.m. and of the engine's efficiency) as well as of the hydrodynamic characteristics of the boat's hull.
An effective answer to these problems is given by the so-called variable pitch propellers, i.e. propellers wherein the orientation of the blades when the propeller is driven by the engine may be adjusted, obviously within certain limits, to particular characteristics and/or conditions of use.
There is a category of commercially available propellers known as variable pitch, feathering propellers which fit in particular the needs of auxiliary engine propulsion systems for sailing-boats.
These known propellers commonly comprise a pinion-hub keyed by means of a conical key joint on a rotary drive shaft, said pinion-hub having a coaxial conical gear, at least two and more preferably three propeller blades, each having a conical planet pinion at the base thereof meshing with said conical gear of the pinion-hub, are journalled through a hub's casing free to rotate about the hub through a limited arc of circumference. Each blade is free to rotate about the axis of their conical pinion base in a planet-wise manner around said conical gear of the pinion-hub for two opposite angles (starting from a neutral position of the blade whereat the faces of the blade are substantially parallel to the axis of the propeller shaft) presettable by stop means, under the hydraulic forces caused, respectively, by the rotation in a forward drive sense and in a reverse drive sense of the drive shaft. These stops determine the pitch of the propeller in the two senses of rotation. The casing is formed by sectors joined together by means of tangential stud screws and houses the pinion-hub and the planet pinions of the blades, which are journalled through holes of the casing formed along the coupling faces of the sectors which form the casing. The latter may rotate about said pinion-hub through either of said two opposite angles, from said neutral position of the blades, together with a planet-wise rotation of the blades around said pinion-hub and about their own axis. The two opposite angles of rotation are preset by stop means which may be formed by a radially extending tooth or sector solidly connected to said casing cooperating with a radially extending tooth or sector solidly connected to the body of said pinion-hub so as to determine by abutment of one tooth with the other stops for both senses of relative rotation.
Propellers of this type are described in U.S. Pat. No. 4,047,841 and U.S. Pat. No. 4,140,434. In these known propellers the pitch could not be modified but through a complete disassembly of the propeller, thus requiring hoisting the boat and of the water for changing the pitch. In a prior Italian patent application No. 83647 A/87, filed on Aug. 11, 1987, assigned to the present applicant, a feathering propeller with a pitch adjustable without grounding the boat and without disassembling the propeller is described. The propeller disclosed in this prior application made use of a thimble meshing with an extremity of the body of said pinion-hub and held engaged therewith by a spring abutting against a closing flange of the casing of the propeller through which flange was mounted an ogive-shaped terminal having a central hole through which a stem solidly connected to said thimble could pass through and emerge from the apex of the ogive terminal. By means of a suitable key this stem could be pulled out in order to disengage said thimble from said pinion-hub and re-engage the thimble on the pinion-hub after having varied their relative angular position, thus changing the pitch of the propeller.
Also this propeller, though having advantages in respect to the previously known propellers, has the drawback of being necessarily disassembled in order to be mounted and dismantled from the drive shaft of the boat and moreover it is necessary to use a key for adjusting the pitch. Moreover as the other propeller of the prior art, the propeller generates a relatively high level of vibrations which fact is imputable in a large measure to the way the blades are journally mounted through the casing, whereby the flexural forces are borne by the tangential stud screws used for joining together the sectors which form the casing, moreover at start-up and reversal of the sense of rotation of the propeller, the casing dragging teeth, by ramming one against the other over said stop surfaces, generate a strong banging noise and a rapid wear of the abutment surfaces of said stops.